Shaping of Fuel Delivery Characteristics for Solenoid Operated Diesel Engine Gaseous Injectors

Solenoid operated gaseous injectors, when compared to conventional liquid fuel diesel injectors, differ in the way the fuel dose and its discharge rate are controlled. While in conventional diesel systems, the fuel dose and its injection rate depends on the fuel injection pump effective stroke and on the plunger diameter and velocity, the solenoid injectors operate in an “on-off” manner which limits the ability to control the gas discharge rate, resulting in its profile to be basically rectangular in shape. To reduce the gas injection rate at the beginning of the injection process in order to suppress the “diesel-knock” phenomenon, similar procedures as used in diesel engines could be implemented. One such approach is to use a throttling type pintle nozzle, and another method is to use a double-spring injector with a hole nozzle. The rationale for using such nozzle configurations is that gaseous fuels do not require atomization, and therefore, can be injected at lower discharge velocities than with liquid fuels.

The gas delivery characteristics from a solenoid injector has been computer-simulated in order to assess the impact of the investigated three modes of fuel discharge rate control strategies. The simulation results confirmed that the gas dose and its discharge rate can be shaped as required. An experimental set-up is described to measure the gas discharge rate using a special gas injection mass flow rate indicator with a strain-gage sensor installed at the entry to a long tube, similar to that proposed by Bosch for liquid fuel volumetric flow rate measurements.